There is no techincal reason that you have to renumber unless you want them all consecutive. I've got servers where there are IPs for 4 different subnets running of the same ethernet interface on Linux

Well, the Accounts person was under the impression that it wasnt possible to have more than one subnet per server... He is getting me the IP's I requested, and letting the techs add them to my account.

Originally posted by The Prohacker Thats if you are on a small network.. Larger networks will have multiple boarder and core routers.. Also VLANs can limit you on what kind of IPs you can bind...

That is true under certain circumstances, but....
Your ISP should be able to route additional netblocks to the gateway IP of your existing netblock and associated VLAN.
The netblocks they route should not be associated with other VLANS already configured on the switch.
For example:
Let's say they assigned you a /27 (123.123.123.0/27)
And this is bound to a VLAN interface you use. It's gateway/router IP is 123.123.123.1
The ISP should be able to do this:
ip route 222.222.222.0 255.255.255.224 123.123.123.1

Doing this will send an additional /27 from a different network over your existing 123.123.123.0/27 down to your switch or server.
Then all you need to do is configure machines connected to your small switch, hub or whatever to IP's on the 222.222.222.0/27 network and tell them to use 123.123.123.1 as the gateway to get out.

I don't know wht your ISP can't do this. It is totally normal.... unless *ALL* of their IP space is already assigned to different VLAN interfaces on their switch. In which case they would not have free netblocks available for this type of routing.